Linear motors are known from U.S. Pat. No. 5,642,013 A, which describes how such drives can be designed in order to avoid or at least significantly reduce cogging forces. In order to cool these motors, that patent proposes to provide cooling channels between the coil-carrying teeth of the iron core. However, such cooling channels reduce the fill factor of the spaces between the teeth. The power of a motor cooled in this manner is lower than that of a motor having a higher fill factor.
U.S. Pat. No. 5,864,187 describes a linear motor that is cooled from the rear side of the lamination stack; i.e., the side opposite the teeth and coils. For this purpose, the epoxy-resin-potted iron core is disposed in an actively cooled metal frame having cooling channels formed in the rear side thereof; i.e., the side facing away from the teeth and coils of the iron core. In an exemplary embodiment, the coolant inlet and outlet are disposed side by side at the same end of the linear motor. A cooling channel extends in a meandering path to the opposite end of the linear motor and back, so that the cooling effect is uniformly distributed over the entire length of the motor. However, producing such meandering cooling channels requires difficult milling operations because of the numerous changes in direction.
U.S. Pat. No. 6,731,028 describes a cooling plate for the primary part of a linear motor, which cooling plate is disposed on the rear side of the primary part. The area between the winding end turns projecting from the lamination stack is filled with a thermally conductive potting compound. The cooling plate has cooling channels of relatively large cross-sectional area formed therein. Therefore, the cooling plate cannot be made very flat and, therefore, adds significantly to the overall height of the primary part. Retrofitting such a cooling plate changes the air gap of the linear motor significantly, or is not possible due to space limitations.